Working in Bolivia’s mines is a family business. That’s what Italian photographer Simone Francescangeli saw when he traveled to the city of Potosí of about 250,000 to document the daily lives of miners.

They’re part of a centuries-old enterprise to extract silver, tin, zinc and gold from the mountains. He was struck by the harsh and sometimes dangerous conditions the miners work in — and by the number of children he saw working in the mines. Some were teenagers. One youngster said he was 11 years old.

In Potosí, many children work in mines, often joining their fathers or other family members in the tunnels when they’re not in school, says Andrea Marston, a researcher at University of California, Berkeley who studies Bolivian mining cooperatives. The money they earn allows them to play a part in supporting their families.

“Miners are scraping by,” says Marston. “It’s more like a family farming structure. Kids are helping out their families rather than working on their own.” Up to a point, they’re legally allowed to do so. In Bolivia, kids must be 14 years old to work, though some exceptions are made for less dangerous jobs.

But the policy is not well enforced, according to the U.S. Department of Labor, which estimates nearly a quarter million Bolivian children ages 7 to 14 work and that these youngsters “engage in the worst forms of child labor, including in mining.”

“Part of the reason there’s no enforcement is because mining cooperatives have been pretty supportive of the government,” Marston says. “They also have a reputation for being violent.” In 2016, miners kidnapped and killed a government official during a strike over labor issues.